A large body of art exists in the art of anti-skid control systems for the braking of braked vehicles. In general, such devices are intended to avoid or prevent wheel-lock in the driver's operation of a wheel braking system, while both improving lateral stability and reducing the braking distance within which the vehicle is stopped. In other words, the effects of overcontrol (due to the operator's performance limitations) are avoided without increasing the stopping distance. A review of representative prior art is included in U.S. Pat. No. 3,790,227 issued to L. C. Dozier for Brake Control System. Further related art is also disclosed in copending application Ser. No. 514,974 filed Oct. 15, 1974 (now U.S. Pat. No. 3,930,688) and assigned to Rockwell International Corporation, assignee of the subject application.
In general, such prior art is directed to the prevention of jack-knifing (due to loss of lateral stability) in tractor-trailer combinations, as well as in minimizing the stopping distances therefor, and are thus intended to cooperate with the air brake type systems normally employed on such vehicles. Such air brake type systems demonstrate a slower dynamic response than the hydraulic systems employed on smaller conventional passenger type automobiles, due to the increased compressibility of the gaseous fluid employed over that in a hydraulic system. Therefore, prior art anti-skid control systems may involve a single control mode representing compromise of the control requirements for a limited combination of vehicle type, vehicle loading and road condition; or may employ several control modes alternatively and include means for switching between such modes as the vehicle response (i.e., combinations of wheel speed and acceleration values) manifests changes in vehicle condition or road condition. In such latter, self-adaptive type of system, the longer vehicle response time, relative to the shorter times for electronic device switching and computing, permits the use of fairly sophisticated electronic control programming, while the investment and cost of the tractor-trailer and associated cargo warrants the cost of such control sophistication.
That skidding associated with overbraking and which is sought to be avoided by anti-skid brake control systems is caused by the road torque applied to the tire being less than the braking torque applied to the wheel. Similarly, high engine torque-to-vehicle weight ratio vehicles (such as police cars and high performance sport cars) may frequently skid or lose traction when high accelerations are called for by the operator, resulting in swerving, fishtailing and potential loss of vehicle control. Thus, it has been discovered that such high-acceleration control problem is analogous to that of anti-skid braking, in that more road torque is called for than the road-tire combination can provide. Because of this analogy between the acceleration-skid problem and the braking-skid problem, an anti-skid computer may also be adapted to control of an automotive engine, say in conjunction with an electronic ignition control system, to prevent loss of vehicle control while allowing a maximum utilizable acceleration under the specific road-tire conditions actually encountered.